Knology is blocking port 25 inbound and outbound
Knology suddenly started blocking port 25 inbound on their residential cable modem service. Ostensibly this is an anti-spam measure, though it is misguided and poorly aimed. They also block port 25 outbound which makes sense, but accept SMTP connections from inside their network to smtp.knology.net.
If you stay with Knology, your only option for static IP address without ports blocked is to go to business service which starts at more than twice the price of residential service.